SUBCUTANEOUS EROSION 31 



the yet hidden " comb." Erosion of the teeth conglomerate would be 

 infinitesimal; of the interstices grit and disintegrated sands per- 

 ceptible. The mass of the one would endure ; of the other, perish. As 

 this rivulet deepened, the soft material of each interstice tapped would 

 be drawn upon and would sympathetically shrink, whilst the hard 

 would remain unaltered. In process of time this subcutaneous drain- 

 age, this subterranean withdrawal of matter from certain portions of 

 our block, would begin to affect the evenness of its surface. The 

 humus skin of the interstices would slightly sag ; instead of an 

 un wrinkled soil - sheet over the whole of our imaginary slope, dips 

 and hummocks would alternate. As the sag deepened with the con- 

 tinued drain from beneath of its internal material, the height of the 

 hummocks would seem to rise. As a tooth wears through the gums, 

 the hard edges of the rock would appear to shove through the 



" In proportion to the depth of sag the height of the rock walls would seem to rise" 



covering of humus. Unceasing shrinkage of the surface would later 

 reveal low, bare, perpendicular rock walls. Later again, the whole of 

 our once even slope would be an alternation of portions still even 

 and of other portions shrunk and sagged. Uninterrupted subcutaneous 

 erosion of the material of the interstices would year by year continue 

 to deepen the lap, whilst in proportion to the depth of sag the 

 height of the rock walls would seem to rise. At last our imagined 

 block of " comb " country in central Tutira would exist as it does 

 actually exist at this present time, a slope falling towards the east 

 with gorges of perpendicular cliff, between each of whose walls lies 

 a dry sagging lap or fold still unwrinkled on the surface, showing no 

 sign whatever externally of water action. Enormous rainfalls have 

 never gouged waterways in this porous soil-sheet ; no watercourses have 

 furrowed it. Except for pig-rootings and hummocks of overblown 



